The largest state in Nigeria by land area is Borno. It has a land area of 72,767 Km².

The state with the smallest land area is Lagos which has 3,475 Km².

Nigeria’s total land mass is 911,519 Km².

The 10 largest states of Nigeria by land area are:

Borno
Niger
Taraba
Bauchi
Yobe
Kaduna
Adamawa
Kebbi
Kwara
Zamfara

Full list of Nigeria states land size. From largest to smallest

State	Area (Km²)
Borno	72,767
Niger	72,065
Taraba	59,180
Bauchi	48,197
Yobe	44,880
Kaduna	44,217
Adamawa	37,957
Kebbi	36,320
Kwara	33,792
Zamfara	33,667
Sokoto	32,146
Benue	30,755
Kogi	29,063
Oyo	27,036
Nasarawa	26,633
Plateau	26,539
Katsina	23,822
Jigawa	23,415
Cross River	22,112
Kano	20,389
Edo	19,584
Gombe	17,428
Delta	17,095
Ogun	16,850
Ondo	15,019
Rivers	10,361
Bayelsa	9,363
Osun	8,585
Federal Capital Territory, Abuja	7,569
Enugu	7,560
Akwa Ibom	6,788
Ebonyi	6,342
Ekiti	5,797
Imo	5,135
Abia	4,857
Anambra	4,761
Lagos	3,475
Total	911,519

By the time that Nigeria got independence it was a federation of the three regions, namely:

Western
Eastern
Northern

Later on another region was added, the Mid-Western Region.

The Mid-Western Region was formed from the Western Region in 1966, and Lagos, the capital, was effectively governed as an unofficial fourth region outside the bounds of the Western Region.

This brought the number of regions to 4 as follows:

Western
Mid-Western
Western
Northern

Under the short-lived military government of Aguiyi-Ironsi, Nigeria was reorganized under a central government. Following a coup which resulted in Aguiyi-Ironsi’s deposition and assassination, Nigeria was reorganized as a federal country again with three of the regions being divided into newer entities and all first-level subdivisions being renamed as states.

Western Region was divided into:
Lagos
and Western states.

Eastern Region was divided into:
East-Central,
Rivers,
and South-Eastern states;

Northern Region was divided into:
Benue-Plateau,
Kano,
Kwara,
North-Central,
North-Eastern,
and North-Western (Sokoto) states

In 1976, six years after the end of the civil war, the states were further reorganized:

State boundaries and names were also reorganized.

Benue-Plateau state divided into:
Benue
and Plateau states.

East-Central state divided into:
Anambra
and Imo states.
Federal Capital Territory (Abuja) formed from parts of Niger and Plateau states.

North-Eastern state divided into:
Bauchi,
Borno,
and Gongola states.
Niger (Minna) state split from Sokoto.

Western state divided into:
Ogun,
Ondo,
and Oyo states

Akwa Ibom state created from Cross River;
Katsina state created from Kaduna

Abia State created from Imo;
Bendel State divided into Delta and Edo;
Enugu State created from Anambra;
Gongola State divided into Adamawa and Taraba;
Jigawa State created from Kano;
Kebbi State created from Sokoto;
Kogi State formed from parts of Benue and Kwara;
Osun State created from Oyo;
Yobe State created from Borno.

Bayelsa State created from Rivers;
Ebonyi State was formed from parts of Abia and Enugu;
Ekiti State created from Ondo;
Gombe State created from Bauchi;
Nasarawa State created from Plateau;
Zamfara State was created from Sokoto.